This invention relates to an apparatus for controlling a reaction, and more particularly to an apparatus for controlling a plasma etching reaction.
Plasma processing is becoming an increasingly important part of manufacturing processes that require etching. This is particularly true in the semiconductor industry where plasma etching is used for removing layers from a semiconductor wafer or for etching patterns in a layer of material overlying a semiconductor wafer. Plasma processing is used to etch precise patterns in layers of polycrystalline silicon, silicon nitride, silicon dioxide, and the like, using a patterned photoresist layer as an etch mask. Plasma processing is also used for stripping photoresist layers, descumming wafers, or other cleaning steps.
It is desirable to have a highly controlled plasma etch process, and more particularly an automatically controlled process. Various control techniques have been proposed and utilized in the past. These techniques include, for example, merely setting the time for the total reaction; detecting the completion of the reaction using a photodetector; and detecting the onset of etching and then allowing the reaction to continue for a set length of time. While these techniques provide a degree of control, they are inadequate for precise process control and for the detection of the end point of the process. All of the above-mentioned techniques can result in an intolerable amount of overetching and the consequent undercutting of the etched layer. Techniques which detect the end of the etching process, for example, do not account for the fact that the etching may proceed non-uniformly across the workpiece. Those areas of the workpiece at which the reaction proceeds most rapidly are likely to be badly undercut before the detector senses the end of the reaction in those areas where the reaction proceeds more slowly. Accordingly, those techniques used in the past have been inadequate to provide the amount of process control and end-point detection necessary in many etching applications.
It is an object of this invention to provide an improved apparatus for controlling the plasma reaction.
It is a further object of this invention to provide an apparatus for improving uniformity and for decreasing undercutting in a plasma etching process.